Indirect Coupling and Antiresonance of Two Optic Phonons

Abstract

Using Green's function techniques we calculate the spectrum for two optic phonons interacting via anharmonic coupling to two acoustic phonons. The single-phonon density of states, which is related to the first-order Raman spectrum, exhibits a zero (antiresonance) between the individual phonon peaks and yields a line shape in excellent agreement with Scott's recent experimental results for AlP${\mathrm{O}}_4$.